1. Field of the Invention
The present invention relates to a needle assembly and more particularly concerns an improved needle assembly for use with or as part of a hypodermic syringe or other fluid transferring device.
2. Description of Related Information
Hypodermic needle assemblies, including a cannula and a hub, are oftentimes removably attached to syringes for performing a variety of tasks such as the administration of medication to patients and into devices and for the withdrawing of fluid samples from patients and from fluid sources. In some cases the cannula is attached directly to the syringe barrel, thus eliminating the hub. Further, many fluid delivery tube sets, fittings and stopcocks have a standard luer or locking luer fitting so that needle assemblies may be used in a variety of drug delivery systems such as in intravenous (IV) therapy and in a variety of fluid handling laboratory setups. Needle assemblies are also used for blood collection and in industrial applications such as dispensing liquids.
A fundamental requirement for a cannula and hub assembly, and an assembly of a cannula and a syringe barrel, is that the resulting assembly be capable of holding the cannula so that it is firmly connected to the hub or syringe and cannot be easily removed therefrom. Also, the cannula should be substantially aligned with the longitudinal axis of the hub or syringe barrel and not projecting angularly therefrom. An important negative consequence of a misaligned cannula occurs in the manufacturing process because the sharp cannula tip can be extensively damaged by engaging the inside wall of the rigid needle shield when the needle shield is placed over the cannula to engage the hub. Proper alignment between the cannula and the hub and/or syringe barrel is important to help the user properly guide the cannula into the patient's body during injection when reshielding the cannula. Further, the manufacturing process used should not create particles or debris in the lumen of the cannula which may later be injected into the patient presenting a potential health hazard.
From a manufacturing process point of view, it can be undesirable to provide a hub which has a cannula receiving bore which is smaller than the outside diameter of the cannula. It is believed that, unless dimensional tolerances are carefully controlled, forcing the hollow cannula through a smaller bore, especially with a plastic hub, allows the fine edges of the cannula to potentially skive plastic material from the hub inside diameter wherein this material may be later injected into the patient. Also, the forced assembly of a cannula and hub presents quality problems during mass production because of the difficulty in controlling the forces involved. The forces required for cannula insertion may be large enough to bend or buckle the cannula, or drive the cannula too far into the hub or through the hub. This is especially true when many cannula hub assemblies are being processed at the same time. Finally, placing a cannula in a long cannula receiving bore may result in the cannula being at an angular orientation with respect to the hub and/or barrel. This angular orientation is the result of molding tolerances and cannot be adjusted if a more optimal angular relationship is required.
Cannula and hub assemblies wherein adhesive is used to bond the cannula to the hub may also present problems where the hub structure allows the adhesive to nearly contact the open proximal end of the cannula because if the adhesive flows into the cannula lumen there is a potential for clogging the cannula. Also, attempting to apply adhesive deeply into the space between hub and loosely fitting cannula presents quality control problems because the process becomes sensitive to the viscosity, temperature and delivery pressure of the adhesive.
U.S. Pat. No. 3,186,408 to Jacob teaches a cannula and hub assembly wherein the cannula mounting portion of the hub has a greater inside diameter than the outside diameter of the cannula so that the space therebetween can be filled with adhesive. Jacob does not appear to provide structure to assure the alignment of the cannula with the hub. The Jacob design, theoretically, allows the adhesive to cover all of that portion of the cannula which is within the hub and potentially to enter the lumen of the cannula.
U.S. Pat. No. 3,472,227 to Burke teaches an improved cannula hub assembly wherein the proximal end of the cannula is physically engaged in the hub, in an interference or frictional fit, to maintain the relative position between the cannula and the hub. This interference would appear to prevent adhesive from passing through to the proximal end of the cannula. Although Burke provides structure to prevent the undesirable entry of adhesive into the cannula, the structure of Burke neither eliminates the potential for skiving hub material into the cannula lumen nor provides a positive stop to position the cannula within the hub. Burke also appears to provide a structure which will not allow for the angular alignment of the needle after it is positioned within the hub.
Burke, in U.S. Pat. No. 3,523,533, teaches a three piece needle hub assembly which has a snap in limit stop provided to contact the proximal end of the cannula while distally placed inwardly positioned ribs engage the cannula upon insertion. After assembly, adhesive is apparently injected between the ribs to fill the cavity in the hub. Here, Burke's design allows potential for skiving of hub material and provides potential for adhesive to enter the proximal end of the cannula. Further, the additional snap in limit stop adds to the complexity of the cannula hub assembly and increases the number of dimensional tolerances which can negatively affect the alignment of the cannula and the hub, without provision for changing the alignment of the cannula in the hub after assembly and before application of adhesive to the structure.
Burke, in U.S. Pat. No. 3,523,532 teaches another three-piece cannula nd hub assembly which is functionally similar to the above mentioned U.S. Pat. No. 3,523,533 to Burke, except that the third component is snapped in from the distal end of the hub rather than from the proximal end. Here again, there is the potential for skiving hub material into the lumen, and also potential for entry of the adhesive into the lumen of the cannula.
U.S. Pat. No. 3,430,627 to Kitaj illustrates a typical cannula syringe tip assembly wherein the syringe tip contains a bore which is larger than the outside diameter of the cannula providing a space for adhesive to be introduced. The structure illustrated in the Kitaj patent does not provide structure for the alignment of the cannula with the syringe barrel and does not appear to eliminate the possibility of adhesive entering the proximal end of the cannula.
U S. Pat. No. 4,581,024 to Swenson teaches a needle assembly to eliminate potential problems regarding skiving by providing a hub with a passageway which is larger than the needle. Swenson's passageway is enlarged at the distal end of the needle hub so that the adhesive used to assemble the needle to the hub is positioned at the end of the passageway opposite to the open proximal end of the cannula to minimize the possibility of adhesive entering the cannula lumen. Swenson's needle assembly, however, does not allow the controlled adjustment of the angular alignment between the needle cannula and hub.
The prior art teaches a wide variety of structures of cannula and hub assemblies. However, there is still a need for a simple, straight forward, reliable, easily fabricated needle assembly which provides needle hub structure which allows adjustment of the angular alignment between the needle cannula and the hub while providing structure which eliminates or minimizes the potential for adhesive entering the cannula lumen and structure which is less prone to skiving or scraping hub material during the assembly process.